The Experiment
by Starlit Anabelle
Summary: A YYH/RK crossover. What happens when a failed plot from over a hundred years ago is unburied? Two of its veterans are brought back to life to help the team. But in return, sacrifices are made...
1. The Capture

Author's Note-This is my first Yu Yu Hakusho fanfic, so if some of the characters are a little ooc or whatever, don't flame me too badly. I own nothing except Shadow and Amori.  
  
The small, black-haired demon jumped from tree to tree. He glanced over his shoulder. Yes, he was right. Someone or something was following him. He stopped and jumped off a high branch into a snowy clearing, looking around.  
  
A girl with long black hair and blue eyes landed in front of him. She wore a black shirt and black pants. "Well, well, well. It's about time you stopped running, Hiei." She said.  
  
Hiei chose to ignore that. "Who are you?" he asked.  
  
The girl smirked. "That is none of your concern. . ." she said nonchalantly. "But I do need you to come with me."  
  
"To where?" Hiei asked, cocking an eyebrow. "And what if I refuse?"  
  
"Oh, it's nothing really. . .my master is just curious. . .he would like to meet the group that defeated the Saint Beasts." The girl replied. "Oh, and if you refuse, then I'll just have to drag you there myself."  
  
"Hn. I would like to see you try."  
  
"Oh, would you? Well, that could be arranged. . ." the girl said. The girl looked around Hiei. That was when Hiei noticed the black splotches surrounding him and floating up in the air. They looked somewhat like inkblots.  
  
Hiei put his hand on his katana cautiously. The girl looked amused and flicked her hand, leaning against a tree. The splotches all rushed at Hiei. The fire demon whipped out his katana and sliced them in half. The splotches dissolved at the touch of his sword.  
  
The girl clapped. "Very good, very good, Hiei. I see that you were an excellent choice indeed. At least in the field of speed." She said. Before Hiei could question what she meant, her eyes narrowed. "However. . ." she said.  
  
Hiei saw black dots swirl around him and group together in front of him into the shape of a sword. The sword swiped at him but Hiei quickly jumped back. The black katana swiped again but this time Hiei slashed at it- and through it. The black katana was unaffected and thrust at his chest. Hiei dodged and was suddenly enveloped in blackness. The blackness suddenly stretched to a sphere, keeping him trapped inside, and became transparent enough to see through, like black glass.  
  
"In the field of intelligence, you haven't excelled." The girl finished, walking over to him.  
  
Hiei glared daggers at her. "What the hell is this?!" He demanded.  
  
The girl smirked. "There's a reason why they call me the daughter of darkness. I can control shadows and darkness anyway I want. Even making it solid is a simple task for me. By the way, I thought that you might be a bit of trouble, even when trapped, so I added a bit of poisonous gas that will knock you out for a couple of hours, given to me by my master." She said. Hiei believed that; there was an odd smell that seemed somewhat toxic beginning to seep in. "By the way, you asked for my name. It's Shadow."  
  
With that, everything went black.  
  
***  
  
Yusuke sighed and looked up at the gray, bleak sky, his hands behind his head as he walked down the sidewalk. "Man. It's almost Christmas and I still haven't bought Keiko a present. And if that's not enough, it had to snow. I hate snow. . ." he complained. He was in a bad mood. He was late to school, failed a history exam on the Bakumatsu (the same exam he forgot to study for. . .), was yelled at by the teachers, tried to skip a class, got caught by the Keiko, who yelled at him, the teachers found out and yelled at him also, and received detention (that he was currently skipping and was probably going to be yelled at for). And to add to all this, he had just spotted a blue-haired, oar-riding girl flying down from the sky.  
  
He sighed. Boton was coming. And probably with some bad news and another assignment. Today was not turning out to be a good day. He stopped as the girl landed in front of him. "Yusuke, I have some bad news." She said.  
  
'. . .I knew it. . .' Yusuke thought. He nodded and walked into an alley. Boton followed. He turned a corner and stopped. "So what's the problem?" he sighed.  
  
"Hiei's missing." Boton said.  
  
". . .Well that's normal. It's not like he stays in the Spiritworld or anything, right?"  
  
Boton nodded. "Right. But. . .we thought that too, until Koenma got a letter."  
  
Yusuke raised an eyebrow but let Boton continue.  
  
"Whoever the sender was, they said they had Hiei and they want you to come to a specified location." Boton said.  
  
"What do they want?" Yusuke asked, though he already had a feeling what Boton's answer was going to be.  
  
"You. And-"  
  
"And if you don't come on your own, we'll have to take you by force like we did to Hiei." A voice from the shadows finished.  
  
Boton and Yusuke both looked over to the girl leaning against the wall. She walked out of the shadows.  
  
"Who are you?" Yusuke demanded, glaring slightly.  
  
The girl sighed mockingly. "Nobody ever seems to say hello anymore. . . You know, you really should learn how to greet a lady." She said. She closed her eyes and smirked. "Anyway, my master would like to meet you-"  
  
"Yeah right." Yusuke said. "What if I don't come?"  
  
The girl blinked. "Like I said, you'll be taken by force. But I don't think you would want to fight me."  
  
"And why would that be?"  
  
"Well. . .we have Hiei. But we really don't need him. Any two people from your group would be fine. My master has other employees. . .we could kill him and get another person from your group. . .Kurama is our second choice, you know. And don't think I can't capture him. Hiei was easy enough, and Kurama shouldn't be too much harder."  
  
Yusuke glared. "What do you want with me the others?" he demanded.  
  
The girl opened her eyes slightly. "Follow me and you'll find out." She replied simply.  
  
Yusuke hesitated, then turned to Boton. "Get Kurama and Kuwabara. You said there was a specified area mentioned in the letter, right? I'll probably be there. You tell them that." He said silently.  
  
Boton nodded and hopped back on her oar. Before she flew off, she said, "Be careful, Yusuke."  
  
Once she was gone, Yusuke turned back to the girl. He seriously wanted to punch her face in, but if what she said was true, then he'd just have to go along with what she said. At least, for now. . . "Alright." He said. "I'll go."  
  
The girl smiled. "Wonderful." She said. A bubble that looked like the one that formed around Hiei appeared around Yusuke.  
  
"Hey, wait a second?! What the hell is this?!" Yusuke yelled.  
  
"Don't worry. . .It's just my form of transportation." The girl said. The poisonous gas from last time seeped into the bubble, knocking Yusuke unconscious. The bubble and Yusuke shrank until it could fit into the palm of her hand. With that, the girl and the bubble literally melted into the shadows.  
  
*three hours later*  
  
Hiei awoke with a throbbing headache. His eyes opened slightly, only to find that he was changed to a wall and several feet off the ground. "What's this. . .?" he muttered. He thought back to the battle, though his mind was still slightly hazy. "Damn it. . ."  
  
He shook his head, clearing it and awakening himself entirely. He looked around. He appeared to be in a dark laboratory of some sort, only lit up by machinery and such. He tugged on the chains to get free, but. . .  
  
"Those are demon-proof. You can try to get free, but it won't work." a voice said from the darkness. Hiei looked towards the voice. An old man with a long gray beard wearing spectacles walked over to him. His hands were clasped behind his back and his eyes were closed. He wore a lab coat.  
  
The man's eyes opened and he looked up at Hiei.  
  
"Who are you?" Hiei demanded. "What is this?"  
  
"Oh, nothing. . .It won't matter to you once the experiment is finished. That is, if it's successful. If not, then you're free to go."  
  
"I asked you what's going on, old man." Hiei snapped.  
  
"And I told you my answer." The man said. Hiei continued to glare at him. The man finally sighed. "Fine. My name is Professor Amori. This is an experiment of if we can bring the dead back to life."  
  
"And just where do I fit in to all this?"  
  
"We needed a demon with speed like yours. If it does work, the soul we're trying to revive will need a fast body. Basically if the experiment works, then your soul will be forced out of your body and the soul of the one we're trying to bring back will take your body." Amori explained.  
  
"You're mad." Hiei said.  
  
"Honestly, it's not exactly my choice. I'm working for somebody and he demanded this to be done."  
  
"Professor." A voice said, coming out of the darkness. "I'm back."  
  
"Ah, Shadow. Welcome back. Did you get the Urameshi boy?"  
  
"Yes, Professor, I did." Shadow said, dropping the bubble she was holding and letting it shatter.  
  
Hiei's eyes widened. "You." He spat.  
  
Shadow smirked. "I see our little fire demon has awakened."  
  
"Yes, yes, and he's been demanding information since." Amori sighed wearily. "I told him that he won't need to know these things if the experiment succeeds, but he won't listen."  
  
"Aw. . .Poor Hiei." Shadow said mockingly. Hiei watched Yusuke grow back to original size.  
  
"What do you want with him? I thought that you needed just a demon, and that is clearly a human." Hiei asked.  
  
"He's a powerful human though. I have to bring back two souls, not just one. One was an assassin and the other was a gangster." Amori explained as Shadow chained Yusuke up next to Hiei.  
  
"Well now, I suppose now that we've got both of them, we begin the experiment." Said Amori, going up to a computer.  
  
"Experiment. . .? I hate science. . ." Yusuke mumbled, still unconscious.  
  
'Idiot. . .' Hiei thought.  
  
"Now, let's see. . ." Amori said as he pressed a few buttons. Hiei watched a beam pointed at them begin to light up.  
  
A siren began to go off, the lab flashing with red light. Shadow looked up and blinked. "Intruders? They must be your friends. I'll go out to greet them." She said, walking out of the lab. Amori nodded, not looking up from his computer.  
  
'It's undoubtedly Kurama and the idiot.' Hiei thought, watching Shadow leave.  
  
The siren turned off and the only sound heard in the lab was the typing of the professor. Hiei's eyes scanned the lab for anything that could help in releasing him.  
  
***  
  
"Well, that was easy enough." Kuwabara said, looking around at all the fallen demons that had been guarding the entrance.  
  
"Yes. Too easy." Kurama said cautiously as they walked down the hall.  
  
"Hello." Said a feminine voice around the corner. A girl dressed in black stepped in front of them.  
  
"A girl. . .?" Kuwabara asked, confused. The girl nodded.  
  
"That's right. . . But don't think I can't kill you just because I'm a girl."  
  
"Excuse me, but we must pass." Kurama said.  
  
The girl closed her eyes and smirked. "I don't think so." She said. "You see, I'm here to keep intruders out of the lab. . .and that includes you."  
  
Kurama's eyes flickered over to a shadow that suddenly seemed to move. 'Did that shadow just twitch. . .?' he wondered.  
  
"There's no point, anyway. There's probably no one left to save by now." The girl said.  
  
"Urameshi's dead?!" Kuwabara demanded.  
  
"If you call being a wandering soul death, then yes, he is. Along with Hiei, the fire demon. And now. . ." she said, flicking her hand. "You two are unwanted guests. Goodbye." With that, the shadows in the hallway jumped and surrounded them.  
  
Kurama pulled out a rose, changing it into his rose whip as Kuwabara's spirit sword formed. Kurama sliced up a few of the shadows, but they kept regenerating. Kuwabara sliced some up. . .and they didn't regenerate?  
  
"Dammit. . .he's using reiki. . .light. . ." the girl hissed, glaring. Kurama looked glanced over at her, having heard her faintly.  
  
"So it's light you can't stand. You must be a shadow demon." He said. He turned to Kuwabara. "Kuwabara, it's your reiki that's destroying the shadows." He said.  
  
Kuwabara blinked at him. "Oh, really?" he asked.  
  
"Oh. . .forget it. . .like I said, it's not like you have anyone to save now, anyway. You might as well leave. As for me. . .I'm outta here." The girl said, still glaring at them and again melting into the shadows.  
  
Kurama looked over at the door at the end of the hall. "I believe the lab is in there." He said.  
  
Kuwabara nodded as his spirit sword disappeared. "Right."  
  
They ran down the hall, hoping that it wasn't too late to save their friends.  
  
Author's Note-Don't worry. Rurouni Kenshin is going to be in the next chapter, but please review anyway. Ja ne. 


	2. Oro?

Author's Note-Well, I am finally posting more to The Experiment. I don't own RK or YYH. I wish I did. But I do own Shadow, Amori, and any other original characters in here. Oh, and this is the chapter that RK is introduced.  
  
~.~ means thought-speech  
  
Enjoy.  
  
"Back so soon, Shadow?" Amori asked.  
  
Shadow glared at him. "You didn't say that one of them could use reiki in the form of a sword!" she accused him.  
  
"Hm. . .you're right, I didn't." Amori replied distractedly. "Well, I'm done." He looked up at the two boys chained to the wall. "Well, I suppose this is farewell, Hiei and Yusuke." He said.  
  
Two things happened at that moment: The door burst open and Kurama and Kuwabara ran in, stopping as the professor pressed the button and the beam powered up, firing at Yusuke and Hiei.  
  
***  
  
Hiei felt a mental pull. He was in pain, his head feeling like it was about to burst. His vision began fading in and out. 'I can't die! Not like this!' he thought angrily. It suddenly felt someone had punched him in the chest and in the head.  
  
***  
  
"I'm not going to stand around and watch, dammit! Spirit sword!" Kuwabara yelled, the spirit sword forming in his hand and throwing it at the computer. The professor's eyes widened.  
  
"No! Don't do that! If you interrupt it then horrible consequences could occur! I'm telling you don't do it!" he yelled, jumping up.  
  
Kurama watched in shock as two souls inside the beam sped to two of his friends. The spirit sword hit the beam. The beam flickered for a moment, then went out. But the souls were gone.  
  
***  
  
Hiei wearily looked up at the beam, groaning. The headache was still there, and worse than ever, but he felt relieved. 'It didn't work. . .' he thought. He felt relieved until he heard someone. . .someone in his head.  
  
~Oro?~  
  
Hiei suddenly felt a bunch emotions that weren't his in his head, mainly confusion. "What the hell. . .?" he muttered. Kuwabara and Kurama ran up to him and Yusuke.  
  
Kurama glanced at Yusuke. "Yusuke seems to be unconscious. . ." he said. He turned to Hiei. "Hiei, are you all right?" he asked.  
  
"I. . ." Hiei started. "I'm fine, but. . ."  
  
'I just imagined it. There's nothing to worry about.' He thought, despite the emotions still swirling in his head.  
  
"Hey, it looks like you're spacing out or something." Kuwabara stated. Even his voice had a note of concern.  
  
"I'm fine." Hiei insisted. Kuwabara and Kurama didn't look convinced as Kuwabara cut the chains to both Hiei and Yusuke. Only, Hiei didn't land on his feet like he normally would. True, he did feel a bit odd, but he wasn't about to admit that. He sat up but stayed on the ground, not bothering to stand up yet.  
  
"H-Hey!" the professor shouted, running over to them.  
  
~Where is sessha. . .?~ someone wondered.  
  
Hiei's eyes widened. 'I didn't just imagine it. . .' he thought. ~Who the hell are you?!~ he demanded.  
  
~Oro? Sessha is Himura Kenshin. Where is sessha?~ the voice replied.  
  
~You're in my head.~ Hiei replied bitterly.  
  
Silence. Then, ~Sessha is supposed to be dead. . .~  
  
~I know that.~  
  
~How did this happen?~  
  
'Damn that scientist. . .' Hiei thought, watching the professor run over.  
  
"Who are you?" Amori questioned.  
  
"Damn you." Hiei said angrily.  
  
"I'm guessing you're still Hiei. Oh well. It didn't work." Amori sighed.  
  
~Um. . .hello?~ Kenshin asked. Hiei continued to ignore him as he quickly stood up. Hiei grabbed the collar of Amori's shirt.  
  
"Reverse it." He ordered.  
  
Kurama, Kuwabara, Shadow (who was still standing by the computer), and Amori blinked. Finally Amori exclaimed, "You mean it did work? Battousai?" he asked.  
  
Hiei heard Kenshin sigh. "There was a screw up, old man." Hiei replied. He lowered his voice. "I'm still here, but now I have this Kenshin guy stuck in my head."  
  
"Hm. . .that does pose a problem, doesn't it? Two people can't share the same body. . ." Amori said, slightly cheerful and somewhat in thought.  
  
"Exactly. Now reverse it." Hiei repeated.  
  
Amori shrugged. "I can't. I didn't create any way of reversing it in this situation. I'm not even sure if it's possible."  
  
Kuwabara blinked, then turned to Kurama. "Did he just say there's someone else in his body?" he asked.  
  
Kurama nodded. "Yes. . .I'm pretty sure that's what he said. . ." He said, sounding slightly unsure.  
  
"So does this mean that Hiei's a schizophrenic?"  
  
Kurama shrugged.  
  
"You do realize that I'm right here, right?" Hiei asked them irritably.  
  
"We haven't forgotten." Kurama replied.  
  
"So what's happened to Urameshi? The same thing?" Kuwabara asked.  
  
"Probably so." Amori spoke up.  
  
Speaking of Yusuke, he was just beginning to awaken.  
  
***  
  
~What the hell. . . What just happened?!~ A voice demanded.  
  
"Shut up. . ." Yusuke muttered.  
  
~Hey! Hey, kid!~ the voice yelled.  
  
Yusuke opened his eyes slightly, his head pounding. "Man, do I need an aspirin. . ." he muttered.  
  
~A what?~ the voice asked.  
  
"Hey! What's this voice doing in my head?!" Yusuke demanded, jumping up.  
  
"And it appears that Zanza is here, too. . ." said the old man nearby.  
  
~I'm not Zanza anymore. I'm Sanosuke Sagara. . .~ the voice muttered.  
  
"What the hell?! What did you do to me?!" Yusuke yelled.  
  
"He tried shoving your soul out of your body to replace it with another." Hiei replied.  
  
"Well, considering that Zanza and Battousai are actually here, will you two help my master? And I don't want a reply from Hiei and Yusuke, just the other two." Amori said.  
  
~. . .I don't know what's going on. And considering this guy's calling me Zanza, I'm guessing he wants something from me. Tell him no.~ Sanosuke replied.  
  
~Why don't YOU tell him?~ Yusuke demanded.  
  
~Well, would you like me to use your voice?~  
  
~. . .Good point.~ Yusuke said. "Sanosuke said no." 'Hm. . .Sagara. . .where have I heard that name before?' he wondered. He decided to shrug that off and yelled at the professor, "How do I get this voice out of my head?!"  
  
"Yusuke, Hiei, if the process wasn't interrupted by your friends-" the professor started.  
  
"Then we'd be dead." Hiei finished.  
  
Yusuke growled, wanting to pound the professor's head in. Sanosuke seemed to sense this and agree with the kid. ~What the hell is he doing bringing me back to life in a body that's not mine, anyway?! The Spiritworld was just fine. . . ~ he said.  
  
"Kenshin wants to know why you went to all this trouble to bring them back." Hiei said suddenly.  
  
"Because," said a voice from the doorway, "I needed the Battousai and Zanza for their skills, but not Himura and Sagara. They'll only get in my way. Just like they did for my great-grandfather, Shishio."  
  
***  
  
Hiei felt a shock from Kenshin. ~Shishio?!~ he cried.  
  
~You know him?~  
  
~Hai. . .Makoto Shishio was what you could call sessha's successor, sessha supposes.~  
  
~Successor?~  
  
~From the Bakumatsu. He was an assassin, but afterwards he tried to take over Japan. That was in the Meiji Era.~  
  
~I see. And you stopped him?~  
  
~Hai. With help.~  
  
The man who was at the doorway walked over to the others. He had brown hair and brown eyes, and looked around his late thirties. He stopped in front of Hiei. "Hello, Himura." He said. Hiei glared up at him.  
  
The man then said to everyone, "I needed these two deceased fighters from the Bakumatsu to help me carry out Shishio's dream for a new Japan."  
  
~Sessha refuses.~ Kenshin said immediately.  
  
"So, this works." Said the man, glancing over at Amori. Amori gulped and nodded.  
  
"Yes. . .but now. . ." he said.  
  
"But now this invention of yours is broken. No matter. Now is time for the next step of my plan."  
  
"Hey!" Yusuke yelled. "You guys had better fix this right now!"  
  
"By the way, I didn't introduce myself, did I? I'm Kane." Said the man, ignoring Yusuke's yells.  
  
"We don't care!" Yusuke said.  
  
~We can't let him carry out his plans! If he wants a Japan like the one Shishio had planned, then innocent people will die!~ Kenshin cried.  
  
~Shut up, he's just a human.~  
  
~Well. . .aren't you a human too?~  
  
~I'm a demon.~  
  
There was silence. Then, ~Oh.~ There was more silence for a second. ~Where are we?~  
  
~We're in a laboratory, idiot. Can't you see that?~  
  
~All Sessha sees is darkness.~ Kenshin responded. Hiei could feel Kenshin concentrate, then say, ~Sessha can see!~  
  
~. . .That's great and all, but I would really appreciate it if you could get out of my body.~ Hiei said sarcastically.  
  
~Oro. . .Sessha doesn't know how, de gozaru. Sessha apologizes.~  
  
Kane smirked at Hiei. "Is Himura freaking out over fact that I could take over Japan? He should. I may have different plans than my great- grandfather, but the outcome will be the same. Once I bring back the Juppongatana, it should be easy. After all, I have my elite group of humans and my elite group of demons. I even have the descendants of some of the former members ready to help. And you don't have your friends to help you anymore."  
  
~He says he has demons on his side!~ Kenshin said.  
  
~You think I didn't hear that?~  
  
~And the Juppongatana. . .this isn't going to be easy, de gozaru yo.~ Kenshin groaned. ~Oh well. . .at least he won't be able to get help from all of them. . .Anji was on our side, so was Aoshi, Kamatari, and others.but sessha doesn't know about the others. . .~  
  
~What are you babbling about? What is this Juppongatana?   
  
~The Juppongatana was an elite group of swordsmen of Shishio's. Some of them. . .became good. . .but not many. Like sessha said, sessha is pretty sure that Kamatari, Cho, Usui. . .several others, too, will come back to him. If Shishio's plans are carried out, Japan will be thrown into chaos and innocent blood will be spilled.~ Kenshin paused. ~Could sessha speak to him directly?~  
  
~What?~  
  
~Sessha might be able to use your voice to speak to him.~  
  
Hiei didn't like the sound of that. ~I won't let a human control me like a puppet.~  
  
~Sessha does not want to. This will only take a few moments.~  
  
Hiei sighed, annoyed. ~Fine. You have five minutes.~ he replied.  
  
~Arigato.~ Kenshin replied. Hiei felt something in the back of his throat. His mouth moved slightly, then- "Thhh. . .Thiii-"  
  
~. . .You're making me look like an idiot.~  
  
~Gomen nasi. Sessha is trying to speak, but it's been awhile since Sessha has had a physical body.~ Kenshin said.  
  
~Just how long ago did you die, anyway?~  
  
~Sessha can't be sure. Sessha doesn't know the year, de gozaru.~  
  
"Hiei, are you okay?" Kurama asked.  
  
"Thiiis. . .This is Kenthen. Shhh. Kenshhhin. Hiei is al-low-ing ses- sha to u-se his vo-ice." Kenshin said. Hiei thought he sounded like a child learning how to read.  
  
"Kenshin?" Yusuke asked, blinking.  
  
"Yes." Kenshin replied, becoming more used to speaking now. "Yes. This is Him-u-ra Ken-shin. Ses-sha re-fuss to help. It will on-ly take the lives of in-no-cent people."  
  
"So, the Battousai has decided to speak, eh?" Kane said in amusement.  
  
"Please stop your plans. Sessha is asking you now."  
  
~If you borrowed my voice to beg, I'm taking it back now. If you want him stopped, I could probably easily kill him.~ Hiei said, disgruntled.  
  
~No. Sessha can't let you kill him. Sessha took a vow to never kill another person, de gozaru yo.~ Kenshin said.  
  
~You did, but I didn't.~ Hiei shot back. ~I'll do what I want.~  
  
Kane laughed. "I've been planning this for at least five years. You think that I would stop my plans just because the spirit of the Battousai told me to?"  
  
"Please, Kan-e." Kenshin said again. "This is the Mei-ji Er-a. This is a time for peace, not un-neces-sary bloodshed."  
  
"Actually, the Meiji Era ended a long time ago. . ." Kurama spoke up. Hiei felt his eyes widen.  
  
'Damn it. He's learning how to control more than my voice. . .' He thought.  
  
"What year is this?! What happened?!" Kenshin demanded.  
  
"It's the year 2003. . ." Yusuke said slowly.  
  
~Hey.~ Hiei said.  
  
~Oro?~ Kenshin asked.  
  
~I thought you were just going to borrow my voice.~  
  
~Sessha is using more than your voice. . .? Gomen. . .~  
  
~Just make sure it doesn't happen again.~  
  
~Hai.~  
  
Author's Note-Well, there's the second chapter. I'll try to get the next chapter out soon. In the meantime, please review! Ja ne! 


End file.
